For radio communication at microwave frequencies, phase noise is a limiting factor. Phase noise creates even more severe issues in a multiple antenna setting (e.g. in MIMO, Multiple Input Multiple Output system). In a multiple antenna setting, several transmit antennas, each with a different oscillator, are used to transmit signals to several receive antennas operating at the same frequency. As each oscillator introduces a phase noise different from other oscillators at the transmit side, the signals transmitted exhibit a mutual phase difference. There is thus a problem of lack of phase alignment between transmitted signals. One possible solution to this problem is to estimate and compensate for the phase difference at the receiver. However, a wireless communication channel between the transmitter and the receiver introduces various types of impairments which may create issues for compensating at the receiver.
Another solution is to compensate for phase noise at the transmitter using information that is fed back from the receiver to the transmitter. However, such solution suffers from low performance due to the delay in receiving feedback information from the receiver and from overhead due to resources consumed by the feedback information transmitted from the receiver.
Thus, there is a need for a phase adjustment technique addressing at least partly the problems stated above without degrading performance.